The thinning of lamellae in surfactant-free foams with non-Newtonian liquid phase

Thinning rates of liquid lamellae in surfactant-free non-Newtonian gas–liquid foams, appropriate for ceramic or polymer melts and also in metals near the melting point, are derived in two dimensions by matched asymptotic analysis valid at small capillary number. The liquid viscosity is modelled (i) as a power-law function of the shear rate and (ii) by the Ellis law. Equations governing gas–liquid interface dynamics and variations in liquid viscosity are derived within the lamellar, transition and plateau border regions of a corner of the liquid surrounding a gas bubble. The results show that the viscosity varies primarily in the very short transition region lying between the lamellar and the Plateau border regions where the shear rates can become very large. In contrast to a foam with Newtonian liquid, the matching condition which determines the rate of lamellar thinning is non-local. In all cases considered, calculated lamellar thinning rates exhibit an initial transient thinning regime, followed by a t−2 power-law thinning regime, similar to the behaviour seen in foams with Newtonian liquid phase. In semi-arid foam, in which the liquid fraction is O(1) in the small capillary number, results explicitly show that for both the power-law and Ellis-law model of viscosity, the thinning of lamella in non-Newtonian and Newtonian foams is governed by the same equation, from which scaling laws can be deduced. This result is consistent with recently published experimental results on forced foam drainage. However, in an arid foam, which has much smaller volume fraction of liquid resulting in an increase in the Plateau border radius of curvature as lamellar thinning progresses, the scaling law depends on the material and the thinning rate is not independent of the liquid viscosity model parameters. Calculations of thinning rates, viscosities, pressures, interface shapes and shear rates in the transition region are presented using data for real liquids from the literature. Although for shear-thinning fluids the power-law viscosity becomes infinite at the boundaries of the internal transition region where the shear rate is zero, the interface shape, the pressure and the internal shear rates calculated by both rheological models are indistinguishable

Project Report No. 46, Loblolly Pine Plantations in East Texas Two Harvest Schedules No Thinning & Final Harvest at 25 Years Thin at 10 Years & Final Harvest at 25 Years Sawlog/Veneer Wood Flow Comparison, A Simulation

DOES A THINNING AT 10 YEARS WITH FINAL HARVEST AT 25 YEARS INCREASE SAWLOG/VENEER 1000 FLOW? DOES A THINNING AT 10 YEARS WITH FINAL HARVEST AT 25 YEARS INCREASE NET PRESENT VALUE

Growth allocation and stand structure in Norway spruce stands

This thesis is based on analyses of permanent sample plot data gathered over periods of 10-34 years from an experiment in which a wide range of thinning regimes, and thinnings combined with N-fertilisation, were applied to 25 even-aged Norway spruce (Picea abies (L.) Karst.) stands in southern Sweden (56-63 No). At the start of the experiment, before the first thinning, the dominant height was 12-18 m. The overall objective was to evaluate the extent to which growth allocation along the bole and the stand structure of Picea abies stands can be controlled by different silvicultural regimes. To do this the data were used in four studies to evaluate the impact of: thinning and N-fertilisation on stem form and taper (Study I); different thinning regimes on the removal and growth in the diameter at breast height (DBH) of individual stems (Studies II and III); and the thinning regimes on the growth in mean DBH of four classes of the largest stems by DBH ha 1 (Study IV). The studies (ii) and (iii) form a growth model. In stands subjected to different thinning regimes, one model predicts which individual trees will remain at future points in time and an associated model predicts the future DBH of the remaining stems. Separate models were developed for stands thinned from below, stands thinned from above and unthinned stands. In Study IV the actual and genuine increases in the arithmetic mean DBH of the 100, 200, 300 and 400 largest stems by DBH ha 1 associated with six different thinning regimes in periods up to 35 years were compared to the corresponding stems in unthinned stands. The goals of achieving rapid diameter growth and low stem tapering cannot be attained simultaneously as heavy thinnings cause increased tapering, and thus silvicultural regimes must reflect a compromise between these and other production objectives. Trees in thinned and N-fertilised stands had the same taper as trees in equally thinned, unfertilised stands. Heavy thinnings from below promote high frequencies of thick stems and extra heavy thinnings promote high frequencies of extra thick stems. Thinning from above (or no thinnngs) may be an alternative to thinning from below in situations where a main crop consisting of moderately thick stems would be regarded as a satisfactory outcome. The actual mean DBH of larger stems can be increased, compared to the corresponding stems in unthinned stands, by up to 2.6 mm per year if extra heavy thinnings are carried out. The biological response to thinning of thick stems is influenced by the thinning intensity but not by the thinning method. The variation in DBH increases over time but increases more in stands thinned from above and unthinned stands than in stands thinned from below

Aspects of precommercial thinning in heterogeneous forests in southern Sweden

The overall objective of the work underlying this thesis was to suggest and evaluate possible strategies for the tending of young heterogeneous stands of Norway spruce, Scots pine and birch in southern Sweden. Heterogeneity was defined as variation in species composition, height distribution and spatial arrangement of the trees. The influence of stand density after precommercial thinning and timing of thinning on the diameter of the thickest branch was studied for naturally regenerated Scots pine. The branch diameter was found to decrease with increasing number of remaining stems after precommercial thinning. However, leaving very dense stands (> 3000 stems ha-1) resulted only in a minor reduction of the branch diameter. Late precommercial thinning, compared to early, reduced the branch diameter. The influence of the precommercial thinning regime on the crown ratio (living crown length/tree height) was also analysed. To be able to simulate the influence of different management options on the development of the young forest, single-tree growth models was developed for Scots pine, Norway spruce and birch. Height growth and diameter was estimated as a function of tree height, stand and site variables. Growth reduction due to competition was estimated using individual, distance independent indices as well as expressions of the overall stand density. In the third study the influence of stand structure after precommercial thinning on the development of mixtures between Norway spruce and silver birch was simulated. The aim was to identify mixtures that allowed both species to develop well until the first commercial thinning. By leaving birches with an average height slightly greater than spruce at precommercial thinning, a large proportion of competitive birches were available at first commercial thinning, at the same time as the relative diameter distribution of spruce in the mixture was equal to that of a pure spruce stand of the same density. The height difference between the species as well as the species proportion had a decisive impact on volume production. In the fourth study different precommercial thinning strategies were identified and applied to a heterogeneous stand including Scots pine, Norway spruce and birch. Stand development and economical returns over a rotation was estimated using a set of empirical models. The aim of the long-term strategies was: (i) a conifer dominated stand with focus on high production, (ii) a conifer dominated stand with focus on high timber quality, (iii) to preserve the heterogeneous stand structure, (iv) a mosaic pattern by tree species, (v) to reduce the precommercial thinning cost, without jeopardizing the future stand development. The difference in total volume production was found to be relatively small between the strategies. The lowest production was found for the strategies promoting species mixture at tree level (iii) and group level (iv). The net present value was highest for the strategy aiming at high production (ii) and lowest for the strategy aiming at preserved heterogeneity (iii). The minimal precommercial thinning (v) was a less profitable alternative, mainly because of an expensive first commercial thinning. Differences in timber quality were not considered in the simulations. The case study illustrates the possibilities for influencing the structure of a heterogeneous stand through precommercial thinning, as well as the limitations imposed by the initial stand structure

Optimizing crop loading of apples and pears - results 2004-2006 (foliar fertilizers, thinning)

Main topics of the research-project FuE 03OE088 of “Bundesprogramm Ökologischer Landbau” (30.04.2004-31.12.2006) were the testing of foliar fertilizers in organic apples and pears, optimizing lime sulphur for blossom thinning, looking for alternatives to lime sulphur for blossom thinning and looking at different combinations of thinning measures. Only the results of testing foliar fertilizers (carried out by KoGa Ahrweiler and OVB/ÖON Jork) and combinations of thinning measures (carried out by LVWO Weinsberg) are described in this article. Over three years only a small increase in yield was evaluated for the fertilizers Aminosol PS and Wuxal Ascofol (site Ahrweiler, apple variety ‘Elstar’). In Jork (apple variety ‘Holsteiner Cox’) yield could only be judged in 2005 and 2006. Wuxal Ascofol showed some advantage in comparison to the control. At pear variety ‘Conference’ no clear tendencies could be seen, the control had the highest yield. In 2005 the fruitsetting of ‘Conference’ was very low because of bad conditions during blossom

Project Report No. 46, Loblolly Pine Plantations in East Texas Two Harvest Schedules No Thinning & Final Harvest at 25 Years Thin at 10 Years & Final Harvest at 25 Years Sawlog/Veneer Wood Flow Comparison, A Simulation

DOES A THINNING AT 10 YEARS WITH FINAL HARVEST AT 25 YEARS INCREASE SAWLOG/VENEER 1000 FLOW? DOES A THINNING AT 10 YEARS WITH FINAL HARVEST AT 25 YEARS INCREASE NET PRESENT VALUE